The proposed studies will investigate the mechanisms by which agonist-selectivity in G protein activation allows selection of differential therapeutically-relevant signal transduction pathways. Working hypotheses begin with a model of sequential steps of ligand docking to the inactive receptor-GGDP complex; agonist-induced conformational change in the receptor and concomitant conformational change in the G protein resulting in its activation (GDP/GTP exchange); G-alpha or G-betagamma regulation of effectors leading to signal transduction pathway activation. Studies previously supported by this grant demonstrated the G protein selectivity that CB, intracellular domains prefer (IL4 with G-alpha0 or G-alphai3, and IL3 with G-alphai1 or G-alphai2). We further demonstrated that agonists of distinct chemical classes influence these different receptor-G protein linteractions. We propose the testable hypothesis that chemically distinct CB1 ligands and Iphosphorylation modifications define which signal transduction pathway(s) are activated. In Aim 1, we continue to define the types of G proteins that interact with the CB1 receptor, and investigate the necessary receptor domains, and the influence of agonists and phosphorylation. In Aim 2, we investigate the CB 1 receptor intracellular surface structure that interfaces with G proteins and assess modifications imposed by post-translational events, in collaboration with structural biology studies by Jason Burgess at RTI, Intl., Sudha Cowsik, and John (Joong-Youn) Shim. In Aim 3, we assess the potential for agonist-directed signal transduction pathway selection: adenylyl cyclase inhibition, MAPK activation, Ca 2v regulation, and NO production, which represent a diversity in potential signal transduction pathway mechanisms. The opportunity for drug design of agonists to facilitate selective receptor-G protein mediated signal transduction pathways may allow stimulation of neuronal cells in brain regions that regulate beneficial effects such as pain relief and alleviation of spasticity and motor dysfunction of neurodegenerative diseases, versus neurons in brain regions that promote untoward responses such as cognitive dysfunction and memory dysregulation.